Key systems are known in which a particular key is required to be received in a key system as to control an aspect of operation. Many different types of keys are used as, for example, keys to open locks in doors and operate machinery such as automobiles.
In the context of dispensing systems, U.S. Patent Publication US 2006/0124662 to Reynolds et al, the disclosure of which is incorporated herein by reference, teaches an electrically powered key device on a refill container to determine if the refill container is compatible with a fluid dispenser. The refill container provides a coil terminated by one of a number of capacitors and the container is received in a housing that provides a pair of coils that are in spacial relationship with the installed refill coil. By energizing the housing's coil, the other coil detects the unique electronic signature which, if acceptable, permits the dispensing system to dispense material. The system thus utilizes a near field frequency response to determine whether the refill container is compatible with the dispensing system.
Such previously known key devices using near field frequency response suffer the disadvantage that they are relatively complex and require a number of metal coils. This has the disadvantage of precluding substantially the entirety of the key device to be manufactured from plastic material and causes difficulties in recycling.
Photochromic and the related word photochromism are words which do not have a rigorous technical definition.
Photochromic is often defined as describing compounds that undergo a transformation of a chemical species between two forms by the absorption of electromagnetic radiation where the two forms have different absorption spectra, that is, different abilities to absorb electromagnetic radiation in a range of “test wavelengths”, as in wavelength or strength. Often the word photochromic is used to describe a “reversible” reaction where an absorption band of the electromagnetic spectrum, typically in the visible part of the electromagnetic spectrum, changes dramatically in strength or wavelength. Typically, the reaction is a photochemical reaction by the absorption of “activating electromagnetic radiation” in a range of “activating wavelengths”.
However, photochromic compounds can be considered to be either reversible or irreversible. Thus, while many technical definitions refer to photochromism as reversible, in this application and in the following claims:                1. the term “irreversible photochromic” is used to refer to photochemical reactions that yield a permenant change by the absorption of electromagnetic radiation;        2. the term “reversible photochromic” is used to refer to photochemical reactions by the absorption of electromagnetic radiation that are reversible; and        3. the term “photochromic” as used includes reactions which are reversible polychromic as defined in (2) above and reactions which are irreversible photochromic as defined in (1) above.        
The activating electromagnetic radiation absorbed in the photochromic reaction is to be considered as being in a range of activating wavelengths which may be any wavelength electromagnetic radiation but is preferably light, more preferably near visible light, ultaviolet light, and visible light.
The different abilities of the two forms of a chemical species of a photochromic compound to absorb electromagnetic radiation may be different abilities to absorb electromagnetic radiation in any range of test wavelengths which may be any wavelength electromagnetic radiation but is preferably light, more preferably, near visible light, ultaviolet light, infared light and visible light.
The two forms of a reversible photochromic compound may be considered to be an unactivated form in which the compound or dye is in an unactivated state and an activated form in which the compound or dye is in an activated state.
Another somewhat arbitrary requirement of reversible photochromic compounds is that they require the two forms to be stable under ambient conditions for a reasonable time. The timescale of reversion is important for many embodiments of the invention considered in this application, and photochromic compounds may be selected or molecularly engineered with timescale of reversion as may be desired. For example, a reversible photochromic compound in an unactivated state may on receiving an adequate “dose” of activating electromagnetic radiation change from an unactivated state to an activated state and in the activated state will inherently in the absence of the activating electromagnetic radiation inherently return to the unactivated state. As one alternative, the reversible photochromic dye in the activated state may on receiving an adequate “dose” of unactivating electromagnetic radiation change from the activated state to the unactivated state. The timescale of reversion may be the only significant difference between what might be considered an irreversible photochromic compound and reveresible photochromic compound.
Reversion of reversible photochromic compounds may also be affected by the absence or presence of electromagnetic radiation in a range of wavelengths, notably light and therefore by darkness, being the absence of light.
The timescale of reversion of reversible photochromic compounds is often shorter at higher temperatures and accelerated by heating. A close relationship exists between photochromic and thermochromic compounds.
The extent to which photochromic compounds considered to be stable at ambient conditions and particularly thermally stable at ambient temperatures may be significant and photochromic compounds may be selected or can also be molecularly engineered with stability including thermal stability as may be desired.
The time that a reversible photochromic compound may be considered to revert from the activated state to the unactivated state at normal ambient room temperatures, may be referred to as the “reversion time period”. The time that a reversible photochromic compound may be considered to change from an unactivated state to an activated state at normal ambient room temperature may be referred to as the “activation time period”.
The ability of a waveguide containing a reversible photochromic compound in an unactivated state to transmit electromagentic radiation in a range of test wavelength is referred to as the “inherent transmission characteristic” or the “unactivated transmission characteristic”. The ability of a waveguide containing a reversible photochromic compound in an activated state to transmit electromagnetic radiation in the range of test wavelengths is referred to as the “activated transmission characteristic”.
Compounds which are known and can be used as reversible photochromic dye include spiropyrans, spirooxazines, diarylethenes, azobenzenes, photochromic quinones and inorganic photochromics including silver and zinc halides and silver chloride. U.S. Pat. Nos. 4,913,544 and 4,851,530 teach exemplary known photochromic compounds and dyes. Such photochromic compounds and dyes are known for use in a variety of materials including plastic and glass. For example, photochromic dyes sold under the trade mark REVERSACOL by James Robertson Ltd. are dyes which are preferably activated light from 350-410 nm and may be readily incorporated into various materials including low density polyethylene at, for example, 0.05% concentration. Such photochromic dyes may be selected so as to provide for different activation time periods and different reversion time periods for the activated dyes to fade from an activated state with maximum absorbance of test wavelengths of light to an inactivated state with lower absorbance of test wavelengths of light. Such REVERSACOL photochromic dyes may be used in various polymer matrix including polyolefins, vinyls, acrylic resins and styrenes. The preferred usage can be in relatively inexpensive low density polyethylene in the range of 0.1% to 2% by weight.